1. Field of the Invention
This invention relates to a multilayered integral element for the chemical analysis of the blood, and in particular to an element which permits the assay of whole blood, plasma or serum for quantitative analysis of the chemical components of the blood.
2. Description of the Prior Art
Blood samples for use in analyzing the chemical components of blood include whole blood and the fluid part of the blood, i.e., plasma and serum, which are obtained after the laborious operation of removing the colored definitely-shaped components of blood. Needless to say, it would be convenient and desirable to employ a process which permits the use of whole blood per se for simple and rapid quantitative analysis of blood or rush assay of blood, e.g., in emergency cases.
Due to technical difficulties, there has not heretofore been provided a method and an analytical material for chemical quantitative analysis of blood which employs whole blood as the assay sample and which is a simple, rapid and dry method.
Multilayered integral elements for the simple and rapid dry quantitative chemical analysis of the blood which are characterized by a porous spreading layer have been disclosed in, for example, Japanese Patent Application (OPI) Nos. 53888/74, 137192/75, 40191/76 (U.S. Pat. No. 4,042,335, 3488/77 (U.S. Pat. No. 4,066,403), 131786/77 (U.S. Pat. No. 4,050,898), and 24893/78, U.S. Pat. Nos. 3,992,158, 3,526,480 and 3,663,374 and collected papers by J. N. Eikenberry et al from the 10th International Meeting of Clinical Chemistry (Mexico City, Feb. 26 through Mar. 3, 1978). The fundamental construction of these elements as described in U.S. Pat. No. 4,042,335 is the combination of a porous spreading layer and a reagent layer, the latter sometimes being a multilayered unit in which its functions are divided into, for example, a first reagent layer and a second reagent layer or a color developing, color detecting or color receiving layer. Sometimes an intermediate layer called a radiation-blocking layer or a barrier layer is placed between such a plurality of reagent layers. Alternatively, there has been provided a construction in which the spreading layer includes a reagent and thus the spreading and reagent layers are integrated. In any case, these elements are based on the two functional layers, i.e., the spreading layer and the reagent layer.
A blood sample dropped on this type of elements for the chemical analysis of blood diffuses uniformly throughout the porous spreading layer and permeates into the reagent layer through its surface. Since the reagent layer has a system incorporated therein, which, upon reaction with the particular component in blood, ultimately leads to a reaction of color development, coloration or discoloration, the components of blood can be quantitatively analyzed by colorimetry, densitometry, fluorimetry, etc.
Since these known multilayered integral elements for the chemical analysis of the blood are described as applicable to whole blood as well as to serum in the above-mentioned references, tests were conducted using whole blood which revealed that the thickness of the radiation-blocking layer must be about 150 .mu.m or more in order to impart an acceptable radiation-blocking ability since the radiation-blocking material taught in the references chiefly comprises a white pigment and even this thickness is not adequate when the system is wet. It was also found that with an increase in the thickness of the system, its permeability to blood is remarkably affected in addition to the inconvenience in manufacture.